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A three-dimensional map of the hot Local Bubble using diffuse interstellar bands

Abstract

The Solar System is located within a low-density cavity known as the Local Bubble1,2,3, which appears to be filled with an X-ray-emitting gas at a temperature of 106 K (ref. 4). Such conditions are too harsh for typical interstellar atoms and molecules to survive2,3. The diffuse interstellar bands (DIBs), the carriers of which remain largely unidentified5, often appear as absorption features in stellar spectra6,7,8 and can be used to trace interstellar gas. Here we report the three-dimensional (3D) structure of the Local Bubble using two different DIB tracers (λ5,780 and λ5,797), which reveals that DIB carriers are present within the Bubble9,10,11. The 3D map shows low values of λ5,797/λ5,780 inside the Bubble compared with the outside. This finding proves that the carrier of the λ5,780 DIB can withstand X-ray photodissociation and sputtering by fast ions, whereas the carrier of the λ5,797 DIB succumbs. This implies that DIB carriers are more stable than hitherto thought, and that the carrier of the λ5,780 DIB must be larger than that of the λ5,797 DIB12. Alternatively, small-scale denser (and cooler) structures that shield some of the DIB carriers must be prevalent within the Bubble, suggesting that such structures may be an intrinsic feature of supernova-driven bubbles.

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The data that support the plots within this paper and other findings of this study are available from the corresponding author on reasonable request.

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Competing interests

The authors declare no competing interests.

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Peer review information: Nature Astronomy thanks Lucky Puspitarini, Barry Welsh and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Acknowledgements

We wish to thank the Iranian National Observatory and School of Astronomy at IPM for facilitating and supporting this project for the northern part of the observations, and Keele University for their hospitality during the visits of A.F. and A.J. and for their support of the southern observations. Also, we wish to thank all of the staff at La Silla in Chile and the ING staff at La Palma, Spain—scientific, technical and administration—for their assistance. M.B. acknowledges an STFC studentship at Keele University. This research has made use of the SIMBAD database, operated at CDS Strasbourg, France. A.F. would like to thank J. Cami for his comments on the paper.

Author information

The main idea for this work was proposed by J.T.v.L. and M.B. The northern observations (with the INT) were proposed by A.J. and carried out by A.F. and H.G.K. as well as other colleagues within the School of Astronomy at IPM, while M.B. and J.T.v.L. proposed and observed the southern targets (with the NTT). A.F. performed the data analysis and data reduction of the northern observations, while M.B. did the same for the southern sample. A.F. implemented the inverse method on the combined data set, and together with J.T.v.L. and H.G.K. wrote the manuscript. All authors read and commented on the manuscript and contributed to the scientific interpretation.

Competing interests

The authors declare no competing interests.

Correspondence to Amin Farhang.

Supplementary information

Supplementary Information

Supplementary Video 1 caption, Supplementary Figs. 1–6, Supplementary text and Supplementary refs.

Supplementary Video 1

The 3D distribution of the λ5,780 DIB within 200 pc of the Sun. Colours represent the logarithm of volume density of the λ5,780 DIB. The Sun is located at the centre of the map. In this movie, the x axis gives the direction toward the GC and the z axis indicates the direction toward the NGP, perpendicular to the GP. All distances in this animation are in parsecs.

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Fig. 1: Observed DIB spectra within and around the LB.
Fig. 2: λ5,780 DIB distribution in three principal slices.
Fig. 3: ζ and σ cloud distribution within the GP.